1. Field of the Invention
This invention relates generally to an improved biocompatible connector and methods of making same for use in liquid chromatography and other analytical systems, and relates more particularly to a connector with a structural reinforcement and a biocompatible fluid passageway useful in a wide variety of fittings or assemblies, including but not limited to unions, adapters, tees, crosses, manifolds, valves, etc.
2. Description of the Related Art
Liquid chromatography (LC), ion chromatography (IC) and gas chromatography (GC) are well-known techniques used in analytical systems for separating the constituent elements in a given sample. In a conventional LC system, a liquid solvent (referred to as the “mobile phase”) is introduced from a reservoir and is pumped through the LC system. The mobile phase exits the pump under pressure. The mobile phase then travels via tubing to a sample injection valve. As the name suggests, the sample injection valve allows an operator to inject a sample into the LC system, where the sample will be carried along with the mobile phase. LC and related technologies, and associated tubing, ports, fittings, and other components are discussed in U.S. patent application Ser. No. 13/206,873 (published as US 2012/0024411), Ser. No. 13/292,667 (published as US 2012/0223520), and Ser. No. 13/686,260 (entitled “microfluidic interconnect”), each of which is incorporated herein by reference.
In a conventional LC system, the sample and mobile phase pass through one or more filters and often a guard column before coming to the column. A typical column usually consists of a piece of tubing which has been packed with a “packing” material. The “packing” consists of the particulate material “packed” inside the column. It usually consists of silica- or polymer-based particles, which are often chemically bonded with a chemical functionality. When the sample is carried through the column (along with the mobile phase), the various components in the sample migrate through the packing within the column at different rates (i.e., there is differential migration of the solutes). In other words, the various components in a sample will move through the column at different rates. Because of the different rates of movement, the components gradually separate as they move through the column. Differential migration is affected by factors such as the composition of the mobile phase, the composition of the stationary phase (i.e., the material with which the column is “packed”), and the temperature at which the separation takes place. Thus, such factors will influence the separation of the sample's various components.
Once the sample (with its components now separated) leaves the column, it flows with the mobile phase past a detector, which can be built using MEMS technology. The detector detects the presence of specific molecules or compounds. Two general types of detectors are typically used in LC applications. One type measures a change in some overall physical property of the mobile phase and the sample (such as their refractive index). The other type measures some properties of only the sample (such as the absorption of ultraviolet radiation). In essence, a typical detector in a LC system can measure and provide an output in terms of mass per unit of volume (such as grams per milliliter) or mass per unit of time (such as grams per second) of the sample's components. From such an output signal, a “chromatogram” can be provided; the chromatogram can then be used by an operator to determine the chemical components present in the sample. Additionally, LC systems may utilize mass spectrometric detection for identification and quantification of the sample, either in addition to, or as an alternative to, the conventional detectors described previously. Ion chromatography relies on the detection of ions in solution, so most metallic materials in the flow path can create interference in the detection scheme, as they create background ions.
In addition to the above components, an LC system will often include filters, check valves, a guard column, or the like in order to prevent contamination of the sample or damage to the LC system. For example, an inlet solvent filter may be used to filter out particles from the solvent (or mobile phase) before it reaches the pump. A guard column is often placed before the analytical or preparative column; i.e., the primary column. The purpose of such a guard column is to “guard” the primary column by absorbing unwanted sample components that might otherwise bind irreversibly to the analytical or preparative column.
In practice, various components in an LC system may be connected by an operator to perform a given task. For example, an operator will select an appropriate mobile phase and column, and then connect a supply of the selected mobile phase and a selected column to the LC system before operation. In order to be suitable for high performance liquid chromatography (HPLC) applications, each connection must be able to withstand the typical operating pressures of the LC system. If the connection is too weak, it may leak. Because the types of solvents that are sometimes used as the mobile phase are often toxic and because it is often expensive to obtain and/or prepare many samples for use, any such connection failure is a serious concern. A high pressure fitting is further discussed in U.S. patent application Ser. No. 13/038,110 (published as U.S. Patent Publication No. US 2012/0223522 A1), the contents of which are incorporated herein by reference.
Most conventional HPLC systems include pumps which can generate relatively high pressures of up to around 5,000 psi to 6,000 psi or so. In many situations, an operator can obtain successful results by operating an LC system at “low” pressures of anywhere from just a few psi or so up to 1,000 psi or so. More often than not, however, an operator will find it desirable to operate a LC system at relatively “higher” pressures of over 1,000 psi. If a connection does not have sufficient structural strength, it could leak at higher pressures.
Another, relatively newer liquid chromatography form is Ultra High Performance Liquid Chromatography (UHPLC) in which system pressure extends upward to 1400 bar or 20,000 psi. Both HPLC and UHPLC are examples of analytical instrumentation that utilize fluid transfer at elevated pressures. For example, in U.S. Pat. No. 8,173,078 (entitled “Sample Injector System for Liquid Chromatography”), an injection system is described for use with UHPLC applications, which are said to involve pressures in the range from 20,000 psi to 120,000 psi. In U.S. Pat. No. 7,311,502 (entitled “Method for Using a Hydraulic Amplifier Pump in Ultrahigh Pressure Liquid Chromatography”), the use of a hydraulic amplifier is described for use in UHPLC systems involving pressures in excess of 25,000 psi. In U.S. Pat. No. 7,144,502 (entitled “Chromatography System with Gradient Storage and Method for Operating the Same”), a system for performing UHPLC is disclosed, with UHPLC described as involving pressures above 5,000 psi (and up to 60,000 psi). Applicants hereby incorporate by reference as if fully set forth herein U.S. Pat. Nos. 7,311,502; 7,14,502; and 8,173,078.
Given the desirability of need for leak-free connections, conventional connections have been made with stainless steel tubing and stainless steel end fittings. More recently, however, it has been realized that the use of stainless steel components in a LC system can have potential drawbacks in situations involving biological samples, and cannot be routinely used for ion chromatography. For example, the components in a sample may attach themselves to the wall of stainless steel tubing. This can present problems because the detector's measurements (and thus the chromatogram) of a given sample may not accurately reflect the sample if some of the sample's components or ions remain in the tubing and do not pass the detector. Perhaps of even greater concern, however, is the fact that ions from the stainless steel tubing may detach from the tubing and flow past the detector, thus leading to potentially erroneous results. Hence, there is a need for biocompatible connections through the use of a material that is chemically inert with respect to such biological samples and the mobile phase used with such samples, so that ions will not be released by the tubing and thus contaminate the sample. Such connections and tubing are further described in U.S. patent application Ser. No. 13/206,873 (published as US 2012/0024411), the contents of which are incorporated herein by reference.
In many applications using selector/injector valves to direct fluid flows, and in particular in liquid chromatography, the volume of fluids is small. This is particularly true when liquid chromatography is being used as an analytical method as opposed to a preparative method. Such methods often use capillary columns and are generally referred to as capillary chromatography. In capillary chromatography, it is often desired to minimize the internal volume of the selector or injector valve. One reason for this is that a valve having a large volume will contain a relatively large volume of liquid, and when a sample is injected into the valve the sample will be diluted, decreasing the resolution and sensitivity of the analytical method.
Micro-fluidic analytical processes also involve small sample sizes. As used herein, sample volumes considered to involve micro-fluidic techniques can range from as low as volumes of only several picoliters or so, up to volumes of several milliliters or so, whereas more traditional LC techniques, for example, historically often involved samples of about one microliter to about 100 milliliters in volume. Thus, the micro-fluidic techniques described herein involve volumes one or more orders of magnitude smaller in size than traditional LC techniques. Micro-fluidic techniques can typically be expressed as those involving fluid flow rates of about 0.5 ml/minute or less.
As noted, liquid chromatography (as well as other analytical instrument) systems typically include several components. For example, such a system may include a pump, an injection valve or autosampler for injecting the analyte, a precolumn filter to remove particulate matter in the analyte solution that might clog the column, a packed bed to retain irreversibly adsorbed chemical material, the LC column itself, and a detector that analyzes the carrier fluid as it leaves the column. Ion chromatography may also utilize a suppressor column to facilitate detection dynamic range. These various components may typically be connected by a miniature fluid conduit, or tubing, such as metallic or polymeric tubing (for ion chromatography), usually having an internal diameter of 0.003 to 0.040 inch.
Fittings for connecting various LC system components and lengths of tubing are disclosed in prior patents, for example, U.S. Pat. Nos. 5,525,303; 5,730,943; and 6,095,572, the disclosures of which are herein all incorporated by reference as if fully set forth herein. The reliability and performance of threaded fluidic fittings is dependent on the amount of torque applied to tighten (or loosen) the fittings. Methods and systems for controlling the torque applied to fittings have been described in U.S. Provisional Patent Application Nos. 61/609,795 and 61/723,163, the contents of which are herein incorporated by reference.
It will be understood by those skilled in the art that, as used herein, the term “LC system” is intended in its broad sense to include all apparatus and components in a system used in connection with a liquid chromatography system (including but not limited to HPLC or UHPLC), and that the discussion of components in the context of LC systems is exemplary, as the invention may apply beyond LC systems to gas and ion chromatography, as well as in vitro diagnostic (IVD) or environmental analysis, and in other analytical instruments (AI) and systems, and may be made of only a few simple components or made of numerous, sophisticated components which are computer controlled or the like. Those skilled in the art will also appreciate that an LC system is one type of an AI system. For example, gas chromatography is similar in many respects to liquid chromatography, but obviously involves a gas sample to be analyzed. Although the following discussion focuses on liquid chromatography, those skilled in the art will appreciate that much of what is said with respect to LC systems also has application to gas chromatography, ion chromatography, and other types of AI systems and methods. Other such AI systems and methods may include, for example, lab on a chip, printing, sensors, micro chromatography, biochemical detection, mass spectrometry, biological sensing, drug discovery, drug delivery, molecular separation, proteomics, fuel cells, optics and opto-fluidics, and research tools.
Increasing pressure requirements in liquid chromatography have necessitated the use of high pressure fluidic components. For many applications regular stainless steel tubing is typically used to withstand the high pressure, such as those in excess of 12,000 psi or so. However, for some types of analyses (e.g., biological testing and metal/ion analysis), stainless steel or other metals are not desired in the fluid path as the metal could interfere with the testing. For example, some methods use corrosive salts which can be incompatible with steel, and the stainless steel can react at an ion level with the chemicals used in the mobile phase of separation. Additionally, there are some fields of use (e.g., nano-scale or nano-volume analysis), that require very small inside diameters to accommodate the extremely low volumes required by these applications. Such small inside diameters are typically not available in stainless steel or other high pressure tubing. Traditional materials utilized for instruments targeting biochemistry and ion chemistry have been PEEK and fluoropolymer (e.g., PTFE, ETFE, PFA, FEP, and PCTFE). However, such materials are limited in pressure capability by the yield strength of the material.